The exhaust gases generated by a vehicular engine are collected by a manifold securely mounted to the engine. The manifold is further connected to the exhaust system of the vehicle to enable transportation of the exhaust gases to a location on the vehicle from which the exhaust gases can be conveniently and safely dispersed. The exhaust system typically will comprise a catalytic converter to reduce certain noxious pollutants and a muffler to reduce the noise levels associated with the flowing exhaust gases. Many engine configurations require the use of a plurality of exhaust manifolds to be mounted to the engine. These manifolds may lead to a single exhaust system or to entirely separate systems.
The size and shape of the exhaust manifold have become important design criteria in recent years. More particularly, the exhaust manifold must compete for the limited space in the engine compartment of the vehicle with various accessories to the engine and with required pollution control equipment.
One type of prior art exhaust manifold has been cast from an appropriate metallic material. These cast manifolds can result in cost efficiencies for very large manufacturing runs and can be cast into a wide range of possible shapes. However, the cast metal manifolds typically are relatively heavy and thus impose an associated penalty on operational performance. Additionally, the cast metal manifolds function as a heat sink which absorbs the heat of combustion and causes the catalytic converter to light-off more slowly.
Another type of prior art manifold is formed from an array of tubes equal in number to the cylinders on the engine. Mounting plates are welded to one end of each tube to enable the tubes to be mounted over the respective exhaust ports of the engine cylinders. The opposed ends of the tubes are joined together. Tubular exhaust manifolds are generally lighter than cast metal manifolds but require a plurality of complex bends and cuts to be made in each tubular member. The appropriately bent and cut tubular members must then be welded to one another along a plurality of irregularly shaped and often inaccessible locations. As a result, the manufacture of tubular manifolds is a relatively labor intensive process in which there is a significant possibility of error.
A relatively recent improvement over the prior art cast metal manifolds and tubular manifolds is shown in U.S. Pat. No. 4,537,027 which issued to Jon Harwood et al on Aug. 27, 1985 and is assigned to the assignee of the subject invention. The disclosure of U.S. Pat. No. 4,537,027 is incorporated herein by reference. Briefly, U.S. Pat. No. 4,537,027 is directed to a hybrid manifold and a method of forming the same wherein the manifold includes stamp formed, tubular and machined parts. The manifold disclosed in U.S. Pat. No. 4,537,027 comprises a generally planar inlet flange adapted to be mounted on the engine and having at least one exhaust port extending therethrough to be in register with at least one cylinder of the engine. A stamp formed sheet metal inner shell is formed with a plurality of inlet apertures disposed to be in register with the associated exhaust ports of the planar inlet flange. The manifold disclosed in U.S. Pat. No. 4,537,027 further comprises a stamp formed sheet metal outer shell attached to the inner shell to define an exhaust chamber therebetween. The outer shell includes an outlet aperture extending therethrough to which an outlet tube is welded. The outlet tube is adapted to be connected to the exhaust pipe of an appropriate exhaust system on the vehicle. The manifold shown in U.S. Pat. No. 4,537,027 provides many desirable advantages including a relatively light weight, a relatively low cost, an ability to conform to virtually any available space envelope and a relatively easy manufacturing and assembly process. More particularly, the assembly of the components of the manifold disclosed in U.S. Pat. No. 4,537,027 can be designed with a weld line between the stamp formed sheet metal inner and outer shells that is very accessible and well suited to automation. The manifold of U.S. Pat. No. 4,537,027 also requires the welding of the stamp formed sheet metal inner shell to the planar inlet flange at the associated exhaust ports therein.
Although the manifold of U.S. Pat. No. 4,537,027 provides many advantages, it has been desired to further improve manufacturing efficiencies. In particular, it has been desired to provide a more efficient method for forming and connecting the planar inlet flange and the stamp formed sheet metal inner shell. In this regard, it should be noted that the manifold shown in U.S. Pat. No. 4,537,027 shows the formation of a planar inlet flange wherein the opposed surfaces thereof are substantially parallel and planar entirely thereacross. The exhaust ports formed in the inlet flange have sidewalls that typically are machined to define a chamfer at their intersection with the surface of the inlet flange to be adjacent with the stamp formed sheet metal inner shell. The stamp formed sheet metal inner shell was then formed with inlet apertures therein the same size and shape as the exhaust ports of the inlet flange. More particularly, each inlet aperture was stamp formed to define a mounting flange that would telescopingly engage the corresponding exhaust port of the inlet flange. The mounting flange then would be welded to the inlet flange adjacent the surface of the inlet flange opposite the stamp formed inner shell. Despite the functional and manufacturing advantages of the manifold of U.S. Pat. No. 4,537,027, these welds of the inner shell mounting flanges to the planar inlet flange required considerable care. Specifically, any excess weldments disposed on the surface of the inlet flange would have to be machined off to ensure a smooth surface for mounting to the engine. Similarly, in certain applications, the welding material that might spill into the manifold would have to be removed prior to installation of the manifold onto the vehicle. These additional manufacturing steps could impose certain penalties on an otherwise extremely desirable and efficient manufacturing process.
Projection welding has been employed in certain manufacturing processes to secure discrete points on two members to one another. Thus, one of the two members typically is formed with a point-like projection against which the second of the members to be welded is positioned. The electrode of a welding apparatus makes contact with the second member in line with the projection. The projection thus defines the weldment that fuses the two members together.
Projection welding often is used to secure a bracket or stud to a planar surface on a frame, engine block or the like. The projection employed in prior art projection welding processes typically was formed by machining or during the casting of the more massive of the members to be welded. However, stamp formed projections are shown in: U.S. Pat. No. 3,190,952 which issued to Bitko on June 22, 1965; U.S. Pat. No. 3,251,127 which issued to Tonelli on May 17, 1986; U.S. Pat. No. 3,629,544 which issued to Becker on Dec. 21, 1971; and U.S. Pat. No. 4,409,460 which issued to Nishii on Oct. 11, 1983. The prior art did not employ projection welding in the manufacture of exhaust system components. The prior art also does not suggest stamp forming a projection and an aperture in a single stamping process such that the projection defines the periphery of the aperture. Furthermore, the prior art does not suggest projection welding a plurality of annular projections simultaneously. Additionally, the prior art does not suggest the combination of projection welding and a telescoping engagement of members at an aperture to ensure an efficient and clean weld around the aperture.
In view of the above, it is an object of the subject invention to provide an efficient method for manufacturing an exhaust manifold.
It is another object of the subject invention to provide an efficient method for securing the stamp formed sheet metal inner shell of a hybrid exhaust manifold to the inlet flange thereof.
It is an additional object of the subject invention to provide a method for manufacturing a hybrid exhaust manifold that avoids machining operations to remove excess weld material.
A further object of the subject invention is to provide a more efficient method for forming the inlet flange of a hybrid exhaust manifold.
Still another object of the subject invention is to provide a method for manufacturing a hybrid exhaust manifold including an extremely fast and efficient method of joining a stamp formed sheet metal inner shell thereof to the inlet flange.